白话学习MVC(五)Controller的激活

一、概述

　　在此系列开篇的时候介绍了MVC的生命周期 ， 对于请求的处理，都是将相应的类的方法注册到HttpApplication事件中，通过事件的依次执行从而完成对请求的处理。对于MVC来说，请求是先 经过路由系统，然后由一个MvcHandler来处理的，当请求到来时，执行此MvcHandler的ProcessRequest方法（因为已将 MvcHandler类的ProcessRequest方法注册到HttpApplication的事件中，所以事件的执行就触发了此方法）。详细请看之前介绍MVC生命周期的两篇博客。
　　下面我们就以MVC声明周期为主线，来分析下MVC源码

public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState
{
    protected virtual void ProcessRequest(HttpContext httpContext)
    {
        //使用HttpContextWrapper对HttpContext进行封装,封装的目的是为了解耦以获得可测试性.然后从RequestContext.RouteData中提取Controller名称.
        HttpContextBase httpContext2 = new HttpContextWrapper(httpContext);
        this.ProcessRequest(httpContext2);
    }
    
    protected internal virtual void ProcessRequest(HttpContextBase httpContext)
    {
        IController controller;
        IControllerFactory controllerFactory;
        this.ProcessRequestInit(httpContext, out controller, out controllerFactory);//获取到Controler和ControllerFactory实例，并赋值给局部变量
        try
        {
　　　　　　　　　 //Action的调用，下一篇介绍
                //当前Controler对象的Action的创建与执行（执行包括:加载TempData, 创建及执行Action，处理Action返回的ActionResult ，保存TempData数据）
                controller.Execute(this.RequestContext);
                
        }
        finally
        {
            //释放当前Controler对象
            controllerFactory.ReleaseController(controller); 
        }
    }
}

 

二、Controller的激活

 　 　从上述代码中可以看出，对Controller激活的相关的操作是通过MvcHandler类的 ProcessRequestInit 方法来执行，而执行完成后，将获取到Controller和ControllerFactory实例！也就是说这 个 this.ProcessRequestInit(httpContext, out controller, out controllerFactory) 方法才是本片博客的旨在，下面就通过这个方法的内部代码来剖析下Controller的激活的机制！

private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
{
   //使用指定的 HTTP 上下文来添加版本标头。如：添加一个Http Header： HTTP/1.1 200 OK   …   X-AspNetMvc-Version: 2.0…
   this.AddVersionHeader(httpContext);
   this.RemoveOptionalRoutingParameters();
//RequestContext.RouteData中提取Controller名称。如：Home/Index的话，就获取到Home
   string requiredString = this.RequestContext.RouteData.GetRequiredString("controller");

   factory = this.ControllerBuilder.GetControllerFactory();//获取一个用于创建Controller实例的ControllerFactory.默认DefaultControllerFactory
   controller = factory.CreateController(this.RequestContext, requiredString);//根据ControllerFactory创建Controller对象。


   if (controller == null)
   {
     throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture,MvcResources.ControllerBuilder_FactoryReturnedNull,new object[]
        {
            factory.GetType(),
            requiredString
        }));
   }
}
由于使用了out关键字，这个方法中的执行过程中所得到的值，即：赋值给ProcessRequest方法中声明的Controller和ControllerFactory

 显然，上述的代码中这两行代码是重点，代码通过执行一个全局的变量ControllerBuilder的GetControllerFactory方法得到 一个ControllerFactory，然后再通过执行此ControllerFactory的CreateController方法得到 Controller实例！

   factory = this.ControllerBuilder.GetControllerFactory();//获取一个用于创建Controller实例的ControllerFactory.默认DefaultControllerFactory
   controller = factory.CreateController(this.RequestContext, requiredString);//根据ControllerFactory创建Controller对象。

下面就来了解下这两行代码：

1、factory = this.ControllerBuilder.GetControllerFactory();

　 　 this.ControllerBuilder是MvcHandler类的一个属性，属性返回的是MvcHandler类声明的一个 ControllerBuilder类型的字段，属性在返回时会判断当前字段是否为空，如果为空，则调用ControllerBuilder类的静态属性 Current字段，来获取一个ControllerBuilder实例。

namespace System.Web.Mvc
{
    public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState
    {
        //省略其他成员变量
        private ControllerBuilder _controllerBuilder;
        internal ControllerBuilder ControllerBuilder
        {
            get
            {
                if (_controllerBuilder == null)
                {
                    _controllerBuilder = ControllerBuilder.Current;
                }
                return _controllerBuilder;
            }
            set { _controllerBuilder = value; }
        }

        private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
        { 
            //省略其他代码
            factory = ControllerBuilder.GetControllerFactory();
        }
    }
}

 
_controllerBuilder = ControllerBuilder.Current;说明ControllerBuilder是由ControllerBuilder类的静态属性Current获取的，接下来再看一下ControllerBuilder类

namespace System.Web.Mvc
{
    public class ControllerBuilder
    {
        //声明静态字段，执行此类的构造函数
        private static ControllerBuilder _instance = new ControllerBuilder();

        private Func<IControllerFactory> _factoryThunk = () => null;
        private HashSet<string> _namespaces = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

        //暂且理解为是封装ControllerFactory的一个类，通过该类的Current属性来获取当前封装的ControllerFactory实例
        private IResolver<IControllerFactory> _serviceResolver;

        public ControllerBuilder()
            : this(null) //: this(null)表示执行带一个参数的构造函数，并且传入的参数为Null
        {
        }

        internal ControllerBuilder(IResolver<IControllerFactory> serviceResolver)
        {
            //如果传入的参数为null，则实例化一个SingleServiceResolver类并赋值给私有字段_serviceResolver。
            _serviceResolver = serviceResolver ?? new SingleServiceResolver<IControllerFactory>(
                                                      () => _factoryThunk(),
                                                      new DefaultControllerFactory { ControllerBuilder = this },
                                                      "ControllerBuilder.GetControllerFactory");
        }

        public static ControllerBuilder Current
        {
            //获取Controller实例
            get { return _instance; }
        }

        public HashSet<string> DefaultNamespaces
        {
            get { return _namespaces; }
        }

        [SuppressMessage("Microsoft.Design", "CA1024:UsePropertiesWhereAppropriate", Justification = "Calling method multiple times might return different objects.")]
        public IControllerFactory GetControllerFactory()
        {
            //获取ControllerFactory实例
            return _serviceResolver.Current;
        }

        public void SetControllerFactory(IControllerFactory controllerFactory)
        {
            if (controllerFactory == null)
            {
                throw new ArgumentNullException("controllerFactory");
            }

            _factoryThunk = () => controllerFactory;
        }

        public void SetControllerFactory(Type controllerFactoryType)
        {
            if (controllerFactoryType == null)
            {
                throw new ArgumentNullException("controllerFactoryType");
            }
            if (!typeof(IControllerFactory).IsAssignableFrom(controllerFactoryType))
            {
                throw new ArgumentException(
                    String.Format(
                        CultureInfo.CurrentCulture,
                        MvcResources.ControllerBuilder_MissingIControllerFactory,
                        controllerFactoryType),
                    "controllerFactoryType");
            }

            _factoryThunk = delegate
            {
                try
                {
                    return (IControllerFactory)Activator.CreateInstance(controllerFactoryType);
                }
                catch (Exception ex)
                {
                    throw new InvalidOperationException(
                        String.Format(
                            CultureInfo.CurrentCulture,
                            MvcResources.ControllerBuilder_ErrorCreatingControllerFactory,
                            controllerFactoryType),
                        ex);
                }
            };
        }
    }
}

ControllerBuilder

ControllerBuilder